1. Field of the Invention
The invention relates to a data processing apparatus and, more particularly, to an apparatus for digitally modulating input data and outputting.
2. Related Background Art
As such a kind of apparatus, a digital VTR for recording and reproducing a digital signal to/from a recording medium has conventionally been known.
Among such VTRs, particularly, in a digital VTR for an industrial use, when the digital signal is recorded to a magnetic tape, it is necessary to reduce a consumption amount of the magnetic tape by raising a recording density by narrowing a track width as much as possible or the like. As a result of that the recording track width is narrowed as mentioned above, in order to correctly reproduce the recording signal, what is called a tracking such that the head accurately traces the recording track is important.
An apparatus for multiplexing a pilot signal for tracking in the digital VTR to the recording signal has been disclosed in Japanese Patent Application Laid-Open No. 4-255969.
FIG. 1 is a block diagram showing a conventional construction of such a kind of apparatus for multiplexing the pilot signal to the recording signal.
In FIG. 1, a recording signal inputted from an input terminal 601 is outputted to a "0" addition circuit 602 and a "1" addition circuit 603 every 24 bits and is added with "0" and "1" as control bits, respectively. The resultant signals are outputted to 2T precoders 604 and 605. The precoders 604 and 605 interleaved NRZI modulate the data of 25 bits and output the modulated signals to component extraction circuits 606 and 607, bit successive detection circuits 608 and 609, and a selection circuit 611.
Each of the component extraction circuits 606 and 607 calculates a predetermined frequency component or DC component of a pilot signal to be multiplexed in a coupled signal train from the signal train which has already been encoded and a supplied 25-bit information word, to detect a correlation with the pilot signal component, and outputs the encoded signal train and 25-bit information word to a comparison circuit 610.
The comparison circuit 610 compares the component which is supplied from the component extraction circuit 606 and the component which is supplied from the component extraction circuit 607 and outputs a signal indicative of the component having a higher correlation for the pilot signal component to the selection circuit 611.
Each of the bit successive detection circuits 608 and 609 calculates the maximum number of successive bits "0" or "1" in the 25-bit information word supplied and outputs to the selection circuit 611. The selection circuit 611 fundamentally outputs the information word on the side shown by the signal from the comparison circuit 610 in 25 bits which are supplied from the precoders 604 and 605 to an output terminal 612.
However, when one of the maximum numbers which are supplied from the bit successive detection circuits 608 and 609 is, for example, equal to or larger than 10, the selection circuit 611 preferentially outputs the 25-bit information word on the side of the small maximum number to the output terminal 612.
In the conventional apparatus as mentioned above, however, the precoder, component extraction circuit, and bit successive detection circuit are necessary on each of the side for addition of "0" and the side for addition of "1", so that a circuit scale increases.
Further, there is also considered a method whereby the precoder, component extraction circuit, and bit successive detection circuit are shared on both of the "0" addition side and the "1" addition side and are time-divisionally used. In this case, however, since it is necessary to raise an operation clock speed of the apparatus, the costs rise.